Biomedical subjects

Bernd Blasius

Publications and source records attributed to Bernd Blasius.

10 recordsLinked to original sources

PubMed2005

A model for seasonal phytoplankton blooms.

We analyse a generic bottom-up nutrient phytoplankton model to help understand the dynamics of seasonally recurring algae blooms. The deterministic model displays a wide spectrum of dynamical behaviours, from simple cyclical blooms which trigger annually, to irregular chaotic blooms in which both the time between outbreaks and their magnitudes are erratic. Unusually, despite the persistent seasonal forcing, it is extremely difficult to generate blooms that are both annually recurring and also chaotic or irregular (i.e. in amplitude) even though this characterizes many real time-series. Instead the model has a tendency to 'skip' with outbreaks often being suppressed from 1 year to the next. This behaviour is studied in detail and we develop analytical expressions to describe the model's flow in phase space, yielding insights into the mechanism of the bloom recurrence. We also discuss how modifications to the equations through the inclusion of appropriate functional forms can generate more realistic dynamics.

Ecosystem↗

PubMed2005

Quasiregular concentric waves in heterogeneous lattices of coupled oscillators.

We study the pattern formation in a lattice of locally coupled phase oscillators with quenched disorder. In the synchronized regime quasiregular concentric waves can arise which are induced by the disorder of the system. Maximal regularity is found at the edge of the synchronization regime. The emergence of the concentric waves is related to the symmetry breaking of the interaction function. An explanation of the numerically observed phenomena is given in a one-dimensional chain of coupled phase oscillators. Scaling properties, describing the target patterns are obtained.

Journal Article↗

PubMed2005

Extinction risk, coloured noise and the scaling of variance.

The impact of temporally correlated fluctuating environments (coloured noise) on the extinction risk of populations has become a main focus in theoretical population ecology. In this study we particularly focus on the extinction risk in strongly correlated environments. Here, we found that, in contrast to moderate auto-correlation, the extinction risk was highly dependent on the process of noise generation, in particular on the method of variance scaling. Such scaling is commonly applied to avoid variance-driven biases when comparing the extinction risk under white and coloured noise. We show that for strong auto-correlation often-used scaling techniques lead to a high variability in the variances of the resulting time series and thus to deviations in the subsequent extinction risk. Therefore, we present an alternative scaling method that always delivers the target variance, even in the case of strong auto-correlation. In contrast to earlier techniques, our very intuitive method is not bound to auto-regressive processes but can be applied to all types of coloured noises. We strongly recommend our method to generate time series when the target of interest is the effect of noise colour on extinction risk not obscured by any variance effects.

Animals↗

PubMed2004

Synchronization of two interacting populations of oscillators.

We analyze synchronization between two interacting populations of different phase oscillators. For the important case of asymmetric coupling functions, we find a much richer dynamical behavior compared to that of symmetrically coupled populations of identical oscillators. It includes three types of bistabilities, higher order entrainment, and the existence of states with unusual stability properties. All possible routes to synchronization of the populations are presented and some stability boundaries are obtained analytically. The impact of these findings for neuroscience is discussed.

Adaptation, Physiological↗

PubMed2004

Host location in flow by larvae of the symbiotic barnacle Trevathana dentata using odour-gated rheotaxis.

The detection and location of specific organisms in the aquatic environment, whether they are mates, prey or settlement sites, are two of the most important challenges facing aquatic animals. Large marine invertebrates such as lobsters have been found to locate specific organisms by navigating in the plume of chemicals emitted by the target. However, active plume tracking in flow by small organisms such as marine larvae has received little scientific attention. Here, we present results from a study examining host location in flow by nauplius larvae of the barnacle Trevathana dentata, which inhabits the stony reef coral Cyphastrea chalcidicum. The experiments included analysis of larval motion in an annular flume under four conditions: (i) still water, (ii) in flow, (iii) in still water with waterborne host metabolites and (iv) in flow with host metabolites. Our results show that T. dentata nauplii are unable to locate their target organism in still water using chemotaxis, but are capable of efficient host location in flow using odour-gated rheotaxis. This technique may enable host location by earlier, less-developed larval stages.

Analysis of Variance↗

PubMed2004

Chaos in a periodically forced chemostat with algal mortality.

We study the possibility of chaotic dynamics in the externally driven Droop model. This model describes a phytoplankton population in a chemostat under periodic nutrient supply. Previously, it has been proven under very general assumptions, that such systems are not able to exhibit chaotic dynamics. We show that the simple introduction of algal mortality may lead to chaotic oscillations of algal density in the forced chemostat. Our numerical simulations show that the existence of chaos is intimately related to plankton overshooting in the unforced model. We provide a simple measure, based on stability analysis, for estimating the amount of overshooting. These findings are not restricted to the Droop model but also hold for other chemostat models with mortality. Our results suggest periodically driven chemostats as a simple model system for the experimental verification of chaos in ecology.

Eukaryota↗

PubMed2003

Anomalous phase synchronization in populations of nonidentical oscillators.

We report the phenomenon of anomalous phase synchronization in interacting oscillator systems with randomly distributed parameters. We show that coupling is first able to enlarge the frequency disorder leading to maximal decoherence for intermediate levels of coupling strength before reaching synchronization. Anomalous synchronization arises when the natural frequency covaries with nonisochronicity and allows for synchronization control by adjustment of system parameters.

Journal Article↗

PubMed2003

Using nonisochronicity to control synchronization in ensembles of nonidentical oscillators.

We investigate the transition to synchronization in ensembles of coupled oscillators with quenched disorder. We find that small coupling is able to increase the frequency disorder and to induce a spread of oscillator frequencies. This new effect of anomalous desynchronization is studied with numerical and analytical means in a large class of systems including Rössler, Lotka-Volterra, Landau-Stuart, and Van-der-Pol oscillators. We show that anomalous effects arise due to an interplay between nonisochronicity and natural frequency of each oscillator and can either increase or inhibit synchronization in the ensemble. This provides a novel possibility to control the synchronization transition in nonidentical systems by suitably distributing the disorder among system parameters. We conjecture that our results are of relevance for biological systems.

Biology↗

PubMed2003

Auxin transport synchronizes the pattern of cell division in a tobacco cell line.

The open morphogenesis of plants requires coordination of patterning by intercellular signals. The tobacco (Nicotiana tabacum cv Virginia Bright Italia) cell line VBI-0 provides a simple model system to study the role of intercellular communication in patterning. In this cell line, singular cells divide axially to produce linear cell files of distinct polarity. The trigger for this axial division is exogenous auxin. When frequency distributions of files are constructed over the number of cells per file during the exponential phase of the culture, even numbers are found to be frequent, whereas files consisting of uneven numbers of cells are rare. We can simulate these distributions with a mathematical model derived from nonlinear dynamics, which describes a chain of cell-division oscillators where elementary oscillators are coupled unidirectionally and where the number of oscillators is not conserved. The model predicts several nonintuitive properties of our experimental system. For instance, files consisting of six cells are more frequent than expected from a strictly binary division system. More centrally, the model predicts a polar transport of the coordinating signal. We therefore tested the patterns obtained after treatment with 1-N-naphthylphthalamic acid, an inhibitor of auxin efflux carriers. Using low concentrations of 1-N-naphthylphthalamic acid that leave cell division and axiality of division unaltered, we observe that the frequencies of files with even and uneven cell numbers are equalized. Our findings are discussed in the context of auxin transport as synchronizing signal in cell patterning.

Biological Transport↗

PubMed2002

Jamming coverage in competitive random sequential adsorption of a binary mixture.

We propose a generalized car parking problem where cars of two different sizes are sequentially parked on a line with a given probability q. The free parameter q interpolates between the classical car parking problem of only one car size and the competitive random sequential adsorption (CRSA) of a binary mixture. We give an exact solution to the CRSA rate equations and find that the final coverage, the jamming limit of the line, is always larger for a binary mixture than for the unisized case. The analytical results are in good agreement with our direct numerical simulations of the problem.

Journal Article↗